DD249006A5 - HOMOGENEOUS MASS, INCLUDING PARTICULAR CERAMIC MATERIAL - Google Patents

Abstract

A homogeneous composition comprising(1) at least one particulate ceramic material, and(2) a liquid medium,in which the compositin comprises at least 50% by volume of particulate ceramic material, in which the particulate ceramic material and liquid medium are selected such that a test composition has a friction coefficient of less than 0.2, and in which the particulate ceramic material has a mean aspect ratio of less than 1.70, a shaped article produced from the composition, a shaped article from which the liquid medium has been removed, and a product in which the particles of ceramic material have been sintered.

Description

Field of application of the invention

The invention relates to a homogeneous mass containing particulate ceramic material, molded articles made from the mass and products made from the molded articles in which the particles of the ceramic material have been sintered to densify them.

By "particulate ceramic material" in the present specification is meant any solid inorganic particulate material whose particles can be co-sintered by heat application The molded articles and sintered products made from the composition of the present invention can be used as high technology ceramics, advanced ceramics, engineering ceramics, and structural ceramics. in particular as heat exchangers and burner nozzles, in the automotive industry, in capacitors, in piezoelectric devices and as a substrate for integrated circuits.

Characteristic of the known technical solutions

Known is the production of products from particulate ceramic materials by dry compression of the particles under high pressure and subsequent heating of the articles thus formed, wherein the ceramic particles are sintered together. This known method suffers from the disadvantages that high pressures are required, the volume fraction of the particulate ceramic material in the molded article being relatively low (generally not more than 50% by volume, although in exceptional cases, ζ B. using very high pressures , the volume fraction can be up to 60% by volume), and the articles which can be produced are generally small and uncomplicated in shape.

Furthermore, moldable masses of particulate ceramic material containing particulate ceramic material and a liquid medium are known. The liquid medium can be water. Such compositions may also contain a clay, or they may contain an organic polymer that is soluble or at least dispersible in water. The presence of the clay or the organic polymer promotes the formation of a coherent moldable mass. The masses may be sufficiently fluid to be pourable and may be formed by applying a relatively low pressure. The molded articles may be made from such moldable masses by subsequently removing the liquid medium from the mass, burning out any polymer present from the molded article, and sintering the particles of the ceramic material.

Such masses and production methods are of course well known in the ceramics industry. Although such moldable masses can be formed using relatively low pressures (if any), as opposed to dry processing of ceramic materials, it has heretofore been difficult to fabricate molded articles containing such a high volume fraction of particulate ceramic material from such moldable masses. z. B. over 50Vol .-%. When a relatively low volume fraction of particulate ceramic material is further processed, i. that is, when the optional organic polymer is burned out and the particles of the ceramic material are sintered together to obtain a densified product, substantial shrinkage can occur, with cracks occurring in the molded article and the product formed therefrom. Another consequence of using a relatively small volume fraction of ceramic material is that very high temperatures and long residence times in the furnace are required to achieve sintering of the particles of ceramic material, and irregularities in the microstructure of the product may occur mechanical weakness.

Methods are also known for making molded articles from masses containing particulate ceramic material and also a polymeric material as a binder for the particulate ceramic material. Such compositions may be used at elevated temperature, e.g. B. by extrusion molding, and the polymeric material in the resulting molded article can be burned out, and the remaining particles of ceramic material can be sintered. In order to form such masses, an elevated temperature must be used at which the polymeric material is liquid, and prior to sintering the particles of the ceramic material, the polymeric material must be removed from the molded article, e.g. by burning. The polymeric material can occupy a substantial volume fraction of the molded article and burning can produce significant porosity in the molded article.

The following are some examples of the preparation of molded articles from a mass containing particulate ceramic material and polymeric material. JP-PS 55-115436-A describes injection molding or extruding a mass of ceramic or metal powder and a resin of polystyrene, atactic polypropylene, polyethylene, a lubricant and a plasticizer. JP-PS 55-113510-A describes the injection molding or extruding a mass of ceramic or metal powder and a crosslinked with a silane polyalkylene resin.

JP-PS 76-029170-B describes an injection-moldable mass of a ceramic material, such as alumina or zirconia, such as ethyl phthalate or butyl phthalate.

GB-PS 1 426317 describes a castable composition containing ceramic material and atactic polypropylene as a binder. The composition may additionally contain a thermoplastic resin, a plasticizer and / or a lubricant. The organic matter may be decomposed and volatilised by heating the shaped article at 340 to 38O ⁰ C and the final firing to sinter the ceramic material can occur at 1600-1 65O ⁰ C.

In recent years, considerable interest has been focused on the production of "high technology ceramics", also referred to as high performance ceramics, engineering ceramics and structural ceramics.High technology ceramics have good mechanical properties under load, good electrical properties and resistance to high temperatures and corrosive influences The high electrical engineering properties of high technology ceramics allow their use in capacitors, in piezoelectric devices and as a substrate for integrated circuits High technology ceramics can be made from particulate ceramic materials by a process which enhances densification of the Material under high pressure and heating the so-compacted material for the purpose of sintering the ceramic particles together Particle-shaped ceramic material of uniform particle size chosen, wherein the particle size may also be small, z. B. less than 0.5 / xm. By means of a densification and sintering process, a ceramic product can be obtained from such read-out particulate ceramic material, which contains very few voids and has a density of up to 99% of the theoretical maximum. However, such a method has the disadvantage that only products of relatively small dimensions and relatively simple shape can be produced.

An example of such a process is in the Journal of the American Ceramic Society, 67, no. 3, pp. 199-203 (1984). There, the spray-drying of a mass of water, polyvinyl alcohol and toner particles and the compression of the thus spray-dried particles at pressures of 18MPa to 345 MPa is described. The maximum compression achieved in the molded article made from the mass prior to subsequent sintering corresponds to a relative density of up to 50%, d. H. up to 50% of the density of the clay itself.

Object of the invention

The object of the invention is to provide a composition which contains a high volume fraction of particulate ceramic material prior to sintering and which can be molded by methods customary in plastics or rubber technology.

Explanation of the essence of the invention

The invention has for its object to find individual components for the composition of the mass, which then gives a mass with the desired properties.

According to the invention, a composition is provided which contains a high volume fraction of particulate ceramic material and which can be readily deformed by plastic or rubber processing techniques to produce molded articles which are of relatively large dimensions and relatively complicated shapes where the particles of the ceramic material are dense and evenly distributed without requiring high pressures.

According to the present invention, a homogeneous mass is presented which

1. at least one particulate ceramic material and

2. liquid medium

contains, wherein the mass contains at least 50 vol .-% of the particulate material and the particulate ceramic material is selected so that a test mass has a coefficient of friction of less than 0.2 and in which the particulate ceramic material has an average shape factor of less than 1.70 ,

When the particulate ceramic material and the liquid medium are selected such that the mass of the set friction coefficient of less than 0.2 and the particulate ceramic material have the predetermined mean shape factor, it is possible to make the particulate ceramic material and the liquid medium homogeneous To produce mass, which can be easily formed by means of methods of plastic and rubber processing into a molded article of large dimensions and complicated shape, which is a high proportion of particulate ceramic material, for. Over 60 vol.% Or even over 70 vol.%, And to produce from the molded article a sintered product having reliable properties containing a high proportion of ceramic material and whose density is very close to or even close to theoretical density reached.

On the other hand, if a mass contains particulate ceramic material and liquid medium in the same high proportion, and the mass has a coefficient of friction greater than 0.2, and / or the particulate ceramic has a mean shape factor greater than 1.7, the mass is much less plastic, and it may become impossible to make a coherent molded article from the mass by means of plastic or rubber processing techniques. In order to obtain a readily moldable mass, it may be necessary to make it with a much lower proportion of particulate ceramic material. In order to obtain a readily moldable mass, it may be necessary to make it with a much lower proportion of particulate ceramic material. The friction coefficient of the mass is determined by the following method. A mass of ceramic material and liquid medium having the desired volume fraction of particulate ceramic material is thoroughly mixed and the particles of the ceramic material are dispersed, e.g. by high-shear mixer, then the mass is on a flat surface

a layer thickness of at least 18 mm applied. Thereafter, a 13mm diameter cylindrical ram is pressed onto the mass with the entire face of the ram in contact with the mass and the load on the ram is increased to 5000 Newton. At this load, the thickness t of the mass between the ram and the flat surface is determined. The friction coefficient μ is decreasing

• 3 + 13 / t

calculated.

The test must be carried out over a range of feed rates between 1 mm / min and 100 mm / min of the press die, within which range there must be at least one feed rate of the press die where the coefficient of friction is below 0.2.

The test for determining the coefficient of friction can be carried out at room temperature. It can also be carried out at a higher temperature if it fulfills the test conditions.

The particulate form of the ceramic material is also an important factor in determining whether or not the mass is easy to process by means of plastic or rubber processing techniques. The particulate form of the ceramic material and the particle size, i. The maximum expansion is achieved by dispersing the particles in a liquid medium

z. For example, it may be an alcohol, but is preferably a solution of an organic polymeric material in a liquid medium. The dispersion, especially the destruction of aggregates, can be assisted by shearing the dispersion and / or application of ultrasonic vibrations. A sample of the dispersion is then microscopically examined at different magnifications, determining the maximum and minimum extension of at least 100% of the dispersed particles, which calculates the form factor for each particle so tested, i. the ratio of maximum to minimum extent, and determines the mean shape factor of the particles in the sample studied. The mean form factor should be less than 1.70.

The present invention also includes molded articles made from the composition by molding, dried molded articles having the liquid medium or the volatile liquid components of the liquid medium removed from the molded article, and products derived from the dried molded article by heating the same are made for the purpose of sintering the ceramic material particles.

It depends on a number of parameters whether a mass of the selected particulate ceramic material and the liquid medium meets the friction coefficient criterion. These parameters are z. The particle size of the ceramic material, the size distribution of the particles, the shape of the particles, i. the form factor, the degree of aggregation of the particles and the nature of the liquid medium. These parameters are interdependent, and while none of the factors are of paramount importance, the choice of parameters helps to satisfy certain preferred criteria in making a mass meeting the friction coefficient criterion.

Preferably, the particles of the ceramic material should be of relatively small size, for example, less than 5 / xm. Particles of less than 1 μιτι or even less than 0.2 μιη are even more advantageous because the use of such particles allows sintering of the particles of ceramic material at lower temperatures and at higher speeds than otherwise.

The particulate ceramic material may have a monomodal size distribution, that is, all particles are of almost exactly the same size, or a multimodal size distribution, i. that is, the particles have a variety of sizes.

In this case, the above form factor applies to the entire multimodal particle mixture, however, the preferred size criteria are applied to all size groups of the multimodal particle mixture. However, a monomodal particulate ceramic material is preferred because it can be sintered more uniformly than a multimodal particulate ceramic material, so that the product produced from the mass can approach or even approach the theoretical density. Thus, the coefficient of variation of the particle size of the ceramic material, i. H. the ratio of the standard deviation of the size from the mean size is preferably in the range of 0 to 0.5, wherein the size is the largest extent, which was determined microscopically as above.

Preferably should

Vs = A = ObIsO ₁ O

be in which

V _{s is} the coefficient of variation of the particle size,

S _{s is} the standard deviation of mean particle size and

x _{s is} the mean particle size.

The particles of the ceramic material must have an average form factor of less than 1.70. In order to make the mass easier to mold, especially when the mass contains a high proportion of particulate ceramic material, the average shape factor of the particles of the ceramic material should preferably be less than 1.50 and the coefficient of variation of the shape factor, i. H. the ratio of the standard deviation of the form factor to the mean form factor, between 0 and 0.5. The use of such a preferred particulate ceramic material promotes uniform sintering.

Preferably should

V _a = -r ² - = 0 to 0.5

be in which

V _{a is} the coefficient of variation of the form factor,

S _{a is} the standard deviation of the mean form factor and

x, which is the mean form factor.

There are known methods for producing particles of ceramic material having small dimensions, a preferred size distribution and the desired shape factor. Such particles of ceramic material may, for. B.

by controlled hydrolysis of alkoxides, by oxygenolysis of volatile materials such as in a plasma, e.g. B.

Oxygenolysis of aluminum chloride or silicon chloride in a plasma to form alumina or silica by gas-phase hydrolysis of halides, ζ. In a hydrogen-oxygen flame, by controlled precipitation from an aqueous solution of a suitable salt, or by thermal treatment of liquid droplets of precursor material.

The type of liquid medium is an important factor that determines whether the mass meets the friction coefficient criterion.

The liquid medium is preferably at room temperature, i. liquid at 20 ° C., since it is thus generally possible to form the mass at room temperature and no elevated temperatures are required, as required when the composition contains a particulate ceramic material and a polymeric material as a binder, such as polyethylene and atactic polypropylene described above.

The liquid medium can be an aqueous or nonaqueous medium, but for cost and safety reasons (eg.

Non-combustibility), an aqueous medium is preferred.

The liquid medium preferably contains an organic polymeric material in solution or dispersion in a liquid.

The organic polymer material serves as an aid to mixing the components of the composition and as a tool for maintaining the shape of the moldings produced from the moldable mixture. As the organic polymer material, it is preferable to use a water-soluble or water-dispersible material.

The use of a liquid medium consisting of an organic polymeric material dissolved or dispersed in a liquid is preferred because, in the post-processing of the molded articles, liquid of the liquid medium is easily removed by heating at a relatively low temperature, especially if the liquid is water. The use of such a liquid medium also has the further advantage over the use of a polymeric material as a binder in that in the subsequent processing of the molded article made from the mass, only a relatively small amount of organic polymeric material is removed from the molded article by burning got to. Suitable water-soluble polymeric materials are, for. B. cellulose derivatives, ζ. Hydroxypropylmethylcellulose; Polyacrylamide, polyethylene oxide and polyvinylpyrrolidone. A preferred polymeric material particularly suitable for use in the preparation of moldable compositions having the desired coefficient of friction is a hydrolyzed polymer or copolymer of a vinyl ester, especially a hydrolyzed polymer or copolymer of vinyl acetate. The degree of hydrolysis of the polymer or copolymer of vinyl acetate is preferably at least 50%, more preferably in the range of 70 to 90%, especially when the mass is to be processed at or near room temperature.

When the liquid medium consists of a solution or dispersion of an organic polymeric material in a liquid, the concentration of the organic polymeric material depends on a number of factors, e.g. The nature of the organic polymeric material, the nature of the particulate ceramic material, e.g. B. its mean shape factor, and the relative volume ratio of the particulate ceramic material and the liquid medium. In general, a concentration of the organic polymeric material in the liquid medium ranges from 5 to 60% by volume.

The liquid medium of the mass can consist of a liquid and a surface-active substance dissolved therein which promotes the dispersion of the particles of the ceramic material in the mass. The liquid medium may consist of a solution or dispersion of an organic polymeric material in a liquid and a surfactant dissolved in the liquid. In addition, when the liquid medium of the composition contains an organic polymeric material, the liquid medium may contain a crosslinking agent for the organic polymeric material which can be reacted with the organic polymeric material in the molded article, thus preserving the shape of the molded article promotes.

The particulate ceramic material in the mass may be any inorganic particulate material, as long as it can be sintered by the application of heat.

Thus, the particulate ceramic material may be an oxide or oxide mixture of a metallic or non-metallic element, e.g. an oxide of aluminum, calcium, magnesium, silicon, chromium, hafnium, molybdenum, thorium, uranium, titanium or zirconium. The ceramic material may be a carbide of, for example, chromium, hafnium, molybdenum, niobium, tantalum, thorium, titanium, tungsten, uranium, zirconium or vanadium, or a nitride of any of these elements. The ceramic material may also be silicon carbide.

Included within the term "particulate ceramic material" are also those metals which can be heat sintered or fused together in powder form, ie those metals which can be processed by the powder metallurgy technique Suitable metals are aluminum and its alloys, copper and its alloys and nickel and its alloys.

The particulate ceramic material may be a mixture of particles, e.g. A mixture of a particulate metal of particulate metals and / or a particulate ceramic non-metallic material or more of such materials.

In the composition of the invention, the particulate ceramic material is present in an amount of at least 50% by volume, i. at least 50% by volume of the total mass, including any air present. Preferably, the proportion of the particulate ceramic material in the mass should be as high as possible, as long as the moldability of the mass is retained, since the possibility of producing a product having a high density which approaches or approaches the theoretical density, from the Mass is thereby improved. It is possible that the mass of the invention contains more than 60% or even more than 70% particulate ceramic material in the bulk of the mass, and the mass remains moldable. In order to enable the production of moldable masses with such a high proportion of particulate ceramic material, the coefficient of friction of the mass described above should be less than 0.10, preferably less than 0.05.

The composition according to the invention should be mixed homogeneously, ie the particles of the ceramic material should be distributed homogeneously over the whole mass, and the process by which the components of the composition are homogeneously mixed is important for obtaining a composition which is the one mentioned above Criterion of friction coefficient fulfilled. It is in fact possible that a mass consisting of a certain particulate ceramic material and a liquid medium in a certain ratio does not satisfy the friction coefficient criterion because the components of the mass do not

are mixed intensively enough, while the same components in the same ratio result in more intensive mixing to a mass that meets the criterion of the coefficient of friction.

The process by which the components of the mass are mixed to obtain a homogeneous mass is thus important. The mixing is preferably carried out under high shear conditions, e.g. in a screw extruder. Preferably, however, the mixing takes place on a twin roll mill whose rolls rotate at the same or different peripheral speed. The mass can be passed several times through the gap between the rolls, whereby the gap size can be reduced more and more. The gap between the rolls of the roll mill can be reduced to 0.1 mm, so that a high shear force can be exerted on the mass, whereby aggregates of the particulate ceramic material, which may be present in the mass, are broken.

The composition of the invention can be deformed by the process of plastic or rubber processing, z. As by compression molding, extrusion, injection molding and especially by calendering on a twin roll chair in plate form. Thus, the mixing of the components of the mass and the molding of the mass in plate form can take place simultaneously on a twin roll mill.

In order for the mass to be formed at a relatively low pressure, the flow pressure of the composition according to the invention should be less than 1 MPa. The determination of the flow pressure can be made when the friction coefficient of the mass is determined (as described above), wherein the flow pressure Y is defined as

Y = 0.0075FMPa ₍

where F is the Newton force which must be exerted on a 13 mm diameter cylindrical punch to compress the mass from a thickness of at least 18 mm to a thickness of 13 mm.

When the mass becomes a molded article of simple profile, e.g. B. a plate, this molded article can then be converted to a molded article of more complicated shape, for. B. by inserting the plate into a corresponding shape and molding the plate to a shape with more complicated profile in the mold.

The molded article may be further treated to remove the liquid medium or liquid volatile components of the liquid medium from the molded article. Further processing, referred to as drying, may be accompanied by shrinkage of the molded article. It is desirable that the volume shrinkage be equivalent to the volume of the liquid medium or the removed liquid of the liquid medium. Drying shrinkage, which is less than the separated liquid medium or volatile liquid components of the liquid medium, is indicative of voids formed in the dried molded article. The drying can be done in an oven, for. B. at a temperature up to 100 ⁰ C or something above, especially if the liquid medium is water.

The product made from the molded article in which the particles of the ceramic material are melted together can be obtained by heating the article to high temperatures by which the particles of the material are sintered, optionally under pressure. The temperature at which the sintering of the particles of the ceramic material takes place depends on the nature of the ceramic material. This temperature is generally above 1000 ⁰ C and may be above 1500 ⁰ C.

When the liquid medium in the composition of the invention contains an organic polymeric material, this material must be removed from the molded article prior to sintering the particles of ceramic material. The organic polymeric material can be burned out. The burning of the organic polymeric material may be accomplished by progressively increasing the temperature of the dried molded article. The temperature increase should not occur at such a rate that too rapid burning of the organic polymeric material disturbs the structural stability of the molded article.

The temperature to which the molded article must be heated in order to remove the organic polymeric material depends on the nature of this material, but in general a temperature not exceeding 500 ^° C. is sufficient.

embodiment

The invention is further illustrated by the following examples.

In the following examples, the shape factors and average shape factors of the particulate ceramic material and their coefficients of variation, the size and average size of the particulate ceramic material and their coefficients of variation, and the coefficients of friction of the masses containing particulate ceramic material were determined by the methods described above.

The packing rate of the particulate ceramic material in the shaped mass and in the molded articles made from the mass were determined by measuring the dimensions of the mass or article and determining the volume of the mass or article therefrom. From the knowledge of the weight of the particulate ceramic material in the mass or in the article and its density, the volume of the particulate ceramic material in the mass or in the article and hence its volume fraction, ie. H. the packing fraction determined.

The difference between the measured volume of the formed mass or molded article and the volume calculated from the known weights and densities of the components of the mass or article, if any, corresponds to the volume of air trapped in the mass or article.

In each of the examples below, the liquid medium consisted of a liquid component and generally an organic polymeric material. The measured weights of particulate ceramic material and organic polymeric material (if used) were placed in a stirrer and mixed for 1 minute. Then a measured weight of the liquid component, e.g. As water, placed in the mixer and stirred for 30 seconds.

Unless otherwise stated, the resulting crumb was removed from the mixer and placed on a twin roll mill and further mixed thereon by applying the mass several times to the nip between the rolls of the mill, which ran at different peripheral speeds. The gap between the rolls was progressively reduced, and the mass was subjected to high shear.

The homogeneously mixed mass was removed from the roll mill in the form of a film and the dimensions of the film and thus its volume were determined.

Thereafter, the Foliein was heated an oven for 16 hours at 8O ⁰ C, to volatilize the liquid in the film, for example the water, the dried film was removed from the oven and determines the dimensions of the film and thus the volume of the film.

example 1

Components of the mass

Particulate ceramic material

TiO ₂ average form factor x _a 1.49

Standard deviation of the mean

Form factor S ₃ 0.472

Coefficient of variation of the form factor V ₃ 0.32

mean size x _s 0.19 / xm

Standard deviation of the mean size S _s 0.699 μηι

Coefficient of variation of size V ₅ 0.35

Density 4.05 g / cm ³

Organic polymeric material

Hydrolyzed polyvinyl acetate (Gohsenol KH 17S), 80% hydrolyzed. Water.

The components of the mass were mixed in the following volume ratio. TiO ₂ 55.8%

Organic polymeric material 13.1%

Water 31.1%

Coefficient of friction of mass 0.05

The mixture was easily formed into a mass in the form of a coherent foil on a twin roll mill. The packing fraction of the TiO ₂ particles in the sheet-like mass coming out of the roll mill, ie in the formed mass, was 55.8%, which corresponds to the fraction in the original mass and indicates that the film contained no air.

After heating to volatilize the water from the film, the packing ratio of the TiO ₂ particles was 60%, indicating that the volatilization of the water is accompanied by shrinkage.

The molded article formed was removed from the water, was heated at a rate of 1 ⁰ C per minute in an oven to 45O ⁰ C to burn out the hydrolyzed polyvinyl acetate. The product was then 1 hour in an oven at 1300 ⁰ C heated to sinter the TiO ₂ particles. The flexural strength of the resulting sintered product was determined by a three-point bending test.

Bending strength 241 ± 29 MPa

Weibuli Module 8,4

For comparison, a mass of 50% by volume of TiO ₂ and 50% by volume of water, using the same TiO ₂ as used above, was mixed in a stirrer. The mixture was crumbly and quite dry and could not be formed into a coherent homogeneous mass. The friction coefficient of the mixture was 0.39.

Example 2

Components of the mass

Particulate ceramic material

SiO ₂ Mean form factor xa 1.31

Standard deviation of the mean

Form factor S ₃ · 0.217

Coefficient of variation of the form factor V _a 0.167

Mean size x _s 0.13 μ, ηη

Standard deviation of the mean size S _s 0.005 μηπ

Coefficient of variation of size V _s .384

Density 2.2 g / cm ³

Organic polymeric material

Hydrolyzed polyvinyl acetate (Gohsenol KH 17S), 80% hydrolyzed. Water.

The components of the mass were mixed in the following volume ratio. SiO ₂ 63.3%

Organic polymeric material 8.2%

Water 28.0%

Coefficient of friction of the mass 0.1.

The mass was easily formed into a mass in the form of a coherent film on a twin roll mill. The packing fraction of the SiO ₂ particles in the sheet-like mass coming out of the roll mill, ie in the formed mass, was 61%, which is slightly below the volume fraction in the original mass and indicates that the film contained a small amount of air. After heating to volatilize the water from the film, the packing ratio of SiO ₂ particles was 69%, indicating that the volatilization of the water is accompanied by shrinkage. For the purpose of comparison, the above procedure was repeated except that the organic polymeric material was omitted and the volume fraction of SiO ₂ in the mass was 57%. The mass was very hard to shape and could not be formed into a coherent film. The coefficient of friction of the mass was 0.38.

Example 3

Components of the mass

Particulate ceramic material

TiO ₂ as in Example 1

Organic polymeric material

Hydrolyzed polyvinyl acetate as in Example 1

Water.

The components of the mass were mixed in the following volume ratio

TiO ₂ 50%

Organic polymeric material 11.6%

Water 38.4%

Coefficient of friction of mass 0.05

The mean shape factor of the particles of the ceramic material and the coefficient of friction of the mass were below the upper limits specified above, and the mass was easily formed on a twin roll mill into a shaped article in the form of a coherent film.

For comparative purposes, the above procedure was repeated but the TiO _{2 was} replaced by particulate Al ₂ O ₃ with the following characteristics.

Mean form factor x _a 2.45

Standard deviation of the mean

Form factor S ₃ 0.82

Coefficient of variation of the form factor V ₃ 0.33

Mean size x _s 0.49 / im

Standard deviation of mean size S _s 0,257 //.m

Coefficient of variation of size V _s 0.524

Density 4 g / cm ³

Coefficient of friction of the mass 0.46.

The mean shape factor of the particles of the ceramic material of 2.45 and the coefficient of friction of the mass of 0.46 were above the upper limits specified above, and the mass could not be formed on the Zwiliingswalzenstuhl into a coherent film. The mass remained in crumbly form.

As a further comparative example, the above procedure of Example 3 was repeated except that the hydrolyzed polyvinyl acetate was replaced by hydroxypropylmethyl cellulose.

The coefficient of friction of the mass was 0.31.

The average shape factor of the particles of the ceramic material of 1.49 (see Example 1) was below the upper limit indicated above, but the coefficient of friction of the masses of 0.31 was above the upper limit indicated above, and the mass could not on the twin roll mill to a be formed contiguous film. The mass remained in crumbly form.

Example 4

Components of the mass

Particulate ceramic material

SiO ₂ WIe in Example 2

Organic polymeric material

Hydrolyzed polyvinyl acetate as in Example 1

Water.

The components of the mass were mixed in the following volume ratio.

SiO ₂ 50%

Organic polymeric material 6.4%

Water 43.6%

Coefficient of friction of mass 0.04

The mean shape factor of the particles of the ceramic material and the coefficient of friction of the mass were below the upper limits specified above, and the mass was easily formed on a twin roll mill to form a shaped article in the form of a coherent foil.

Example 5

The procedure of Example 2 was repeated except that the organic polymeric material was omitted and the mixture contained 50 vol.% SiO ₂ and 50 vol.% Water. The friction coefficient of the mass was 0.03 and the flow pressure was 0.002 MPa. The mass was liquid and easily moldable.

For comparison, when the proportion of SiO ₂ in the composition was increased to 57% by volume, the friction coefficient increased to 0.38, and the composition was extremely difficult to form.

Example 6

The procedure of Example 2 was repeated except that the organic polymeric material was omitted and the mass contained 50% by volume of SiO ₂ and 50% by volume of glycerol (in place of the water in Example 2). The friction coefficient of the mass was 0.03 and the flow pressure 0.1 MPa. The mass was liquid and easily moldable.

Example 7

Components of the mass

Particulate ceramic material

AI ₂ O ₃ Mean form factor x _a 1,443

Standard deviation of the mean

Form factor S _a 0,367

Coefficient of variation of the form factor V _a . ' 0.25

Average size x _s 0.251 / μm

Standard deviation of mean size S ₅ 0.108 / im

Coefficient of variation of size V ₅ 0.43

Density 3.97 g / cm ³

Organic polymeric material Hydrolyzed polyvinyl acetate as in Example 1 Water.

The components of the mass were mixed in the following volume ratios Al ₂ O ₃ * 50%

Organic polymeric material 16.6%

Water 33.4%

Coefficient of friction of mass 0,03

Flow pressure 0.71 MPa.

The mass was easily formed on a twin roll mill into a coherent film.

The film was heated to volatilize the water, the resulting molded article from which the water was removed was heated to 450 ° C in an oven at a rate of 1 ° C per minute to burn out the hydrolyzed polyvinyl acetate, and then the Heat the article for 0.5 h in an oven to 1 550 ⁰ C to sinter together the AI ₂ O ₃ particles.

The flexural strength of the resulting sintered product was 274 ± 10 MPa.

For comparative purposes, the above procedure was repeated, omitting the organic polymeric material. When the mass contained only 50% by volume of Al ₂ O ₃ , the friction coefficient was 0.21. The mass could not be formed into a coherent film.

Example 8

The procedure of Example 7 was repeated but the mixture contained

AI ₂ O ₃ 52.82 Vol .-%

Organic polymeric material 17.59 Vol .-%

Water 29.57% by volume.

The coefficient of friction of the mass was 0.19 and the flow pressure was 0.26 MPa. The mass was easily formed into a coherent film.

For comparative purposes, the above procedure was repeated but containing the mass

AI ₂ O ₃ 55.15Vol .-%

Organic polymeric material 18.37 Vol .-%

Water 26.47% by volume.

The friction coefficient of the mass was 0.25 and the flow pressure was 5 MPa. The mass could not be formed into a coherent film.

Examples

From the following components a mass was prepared.

TiO ₂ (as in Example 1) 50% by volume

Polyacrylamide 15% by volume

1 g sodium lignosulfonatin

aqueous solution 4.4% by volume

Water 31% by volume.

The coefficient of friction of the mass was 0.06, and the mass could be easily formed into a coherent film.

Example 10

Components of the mass

AI ₂ O ₃ Mean form factor x _a 1.0

Standard deviation of the mean

Form factor S _a ü

Coefficient of variation of the form factor V _a

Mean size x _s 0.074μΓη

Standard deviation of the mean size S _s 0.029 μΐπ

Coefficient of variation of the size V _s 0.39

Density 3.9 g / cm ³

Organic polymeric material Hydrolyzed polyvinyl acetate as in Example 1 Water.

The components of the mass were mixed in the following volume ratio. AI ₂ O ₃ 56.2%

Organic polymeric material 14.9%

Water 28.9%

The coefficient of friction of the mass was 0.03 and the flow pressure 0.71 MPa. The mass was easily formed into a coherent layer.

For comparison, the above procedure was repeated wherein the Al ₂ O _{3 was} replaced by tribasic calcium phosphate having a form factor of 4.7, which is well above the maximum of the composition of the invention. The coefficient of friction of such a mass was low when the components were in the following volume ratio.

Tribasic calcium phosphate 35.7%

Organic polymeric material 18.8%

Water 45.5%

On the other hand, the friction coefficient was high (0.25) when the components of the mass were in the following volume ratio.

Tribasic calcium phosphate 39%

Organic polymeric material 42%

Water 19%

In the former case the mass had a certain plasticity, in the latter case it was not malleable.

Example 11

Components of the mass

SiC, mixture of two grains

Grain 1 Medium Form Factor x _? 1.45

- standard deviation of the mean

Form factor S _a 0.34

Coefficient of variation of the shape factor M ₃ 0.23

Mean size x _s 0.66 ^ m

Standard deviation of the mean size S _s 0.31 μηη

Coefficient of variation of size V _s 0.46

Density 3.2 g / cm ³

Grain 2 Mean form factor x _a 1.46

Standard deviation of the mean

Form factor: 0.45

Coefficient of variation of the form factor V _a 0.31

Average size x _s 0.094μηι

Standard deviation of mean size S _s 0.032 μm

Coefficient of variation of size V _s 0.35

Density 3.2 g / cm ³

Organic polymeric material Hydrolyzed polyvinyl acetate as in Example 1 Water.

The components of the mass were mixed in the following volume ratio. SiC 54%

Organic polymeric material 15%

Water 31% *

The coefficient of friction of the mass was 0.11 and the flow pressure was 0.7 MPa. The mass was easily formed into a coherent film.

For comparison, the mass of the above components in the following volume ratio SiC was 55%

Organic polymeric material 10%

Water 35%

manufactured, d. H. with a reduced proportion of organic polymeric material. The coefficient of friction of this mass was 0.34, and the flow pressure was 1.5 MPa. The mass could not be formed into a coherent film.

Example 12

A mass of TiO _{2 was} prepared as in Example 1, water and a copolymer of polyvinyl butyral and polyvinyl alcohol in the following volume ratio.

TiO ₂ 50.2%

Organic polymeric material 9.15%

Tetrahydrofurfural methacrylate 40.65%.

Coefficient of friction of mass 0,03.

The mass was easily formed into a coherent film.

Claims (22)

1. Homogeneous mass, characterized in that they (1) at least one particulate ceramic material and (2) contains a liquid medium, which mass contains at least 50% by volume of particulate ceramic material, in which the particulate ceramic material and the liquid medium are selected such that a test mass has a coefficient of friction of less than 0.2 and in which the particulate ceramic material has an average form factor of less than Has 1,70. 2. Homogeneous mass according to item 1, characterized in that the particles of the ceramic material have a size of less than 5μΐη. 3. Homogeneous mass according to item 2, characterized in that the particles of the ceramic material have a size of less than 1 μηι. 4. Homogeneous composition according to any of items 1 to 3, characterized in that the coefficient of variation of the particle size of the ceramic material V _{3 is} in the range of 0 to 0.5, wherein V _{8 is} the coefficient of variation of size, S _{3 is} the standard deviation of the mean size, and x _{s is} the mean particle size. 5. Homogeneous mass according to one of the items 1 to 4, characterized in that the mean shape factor of the particles of the ceramic material is less than 1.50. 6. Homogeneous composition according to any one of items 1 to 5, characterized in that the coefficient of variation of the shape factor of the particles of the ceramic material V _{a is} in the range of up to 0.5, wherein V _{a is} the coefficient of variation of the form factor S _{a is} the standard deviation of the mean form factor, and x _{a is} the mean form factor. 7. Homogeneous composition according to one of the items 1 to 6, characterized in that.dos liquid medium is liquid at room temperature. 8. Homogeneous composition according to one of the items 1 to 7, characterized in that the liquid medium is an aqueous medium. 9. Homogeneous composition according to any one of items 1 to 8, characterized in that the liquid medium consists of a solution or dispersion of an organic polymeric material in a liquid. 10. Homogeneous composition according to item 9, characterized in that the liquid medium is an aqueous solution of a hydrolyzed polymer or copolymer of a vinyl ester. A homogeneous composition according to item 10, characterized in that the hydrolyzed polymer or copolymer of a vinyl ester is a hydrolyzed polymer or copolymer of vinyl acetate having a degree of hydrolysis in the range of 70 to 90%. Homogeneous composition according to any one of items 9 to 11, characterized in that the concentration of the organic polymeric material in the liquid medium is in the range of up to 60VoI. -% is. 13. Homogeneous composition according to any one of items 1 to 12, characterized in that the liquid medium contains a surfactant. 14. Homogeneous composition according to any one of items 1 to 13, characterized in that the particulate ceramic material consists of an oxide or oxide mixture of a metallic or non-metallic element. 15. Homogeneous composition according to item 14, characterized in that the particulate ceramic material is selected from the group of the oxides of aluminum, silicon, titanium and zirconium. 16. Homogeneous composition according to any one of items 1 to 13, characterized in that the particulate ceramic material is silicon carbide. 17. Homogeneous composition according to any of items 1 to 16, characterized in that it contains more than 60 vol .-% particulate ceramic material. 18. Homogeneous mass according to one of the items 1 to 17, characterized in that the coefficient of friction is less than 0.10. 19. Homogeneous mass according to item 18, characterized in that the coefficient of friction is less than 0.05. 20. Use of the homogeneous composition according to item 1 to 19, characterized in that it is used for the production of molded articles. 21. Use according to item 20, characterized in that the liquid is removed from the liquid medium. 22. Use according to item 21, characterized in that the particles of the ceramic material were sintered.